vision

layers of the eyeball

fibrous, vascular, and inner layer

fibrous layer contains

sclera and cornea

sclera

85% of the fibrous layer, Provides shape and support, and attaches extraocular muscles for eye movement, Visible as the white part of the eye

cornea

transparent, anterior continuation of the sclera, refracts light entering the eye

vascular layer contains

choroid, ciliary body, iris

choroid

Layer of connective tissue and blood vessels, Nourishes outer layers of the retina

Ciliary Body

Comprised of the ciliary muscle and ciliary processes, Controls lens shape via zonular fibers (suspensory ligament of the lens)

Ciliary Muscle

Smooth muscle fibers in three orientations (longitudinal, circular, radial), Contraction reduces diameter, facilitates lens accommodation for near vision, Relaxation increases diameter, flattening the lens for distance vision

Iris

Eye color determined by the iris.

Circular Fibers (sphincter pupillae)

Innervated by parasympathetic system for constriction.

Radial Fibers (dilator pupillae)

Innervated by sympathetic system for dilation.

Inner Layer

Retina (neural and pigmented layers)

• Neural Layer:

  • Contains photoreceptors, located posteriorly and laterally.

• Pigmented Layer:

  • Supports the neural layer, attached to the choroid.

  • Anterior continuation forms the non-visual retina.

neural layer

Contains photoreceptors, located posteriorly and laterally

Pigmented Layer

Supports the neural layer, attached to the choroid.

Anterior continuation forms the non-visual retina.

Optic Disc

Entry point for the optic nerve, contains no light-detecting cells (blind spot).

Chambers of the Eye

Anterior Chamber: Between cornea and iris.

Posterior Chamber: Behind the iris, anterior to lens.

Aqueous Humor

Nourishes and protects the eye, secreted into the posterior chamber, flows to the anterior chamber, absorbed into canal of Schlemm (scleral venous sinus). & Obstruction can lead to glaucoma due to increased intraocular pressure.

Vitreous Humor

Gel-like substance filling the eyeball, extends from behind the lens to the retina

superior rectus

CN III (oculomotor), and elevation

inferior rectus

CN III (oculomotor), and depression

medial rectus

CN III (oculomotor), and adduction (moves medially)

lateral rectus

CN VI (abducens), and abduction (moves laterally)

superior oblique

CN IV Trochlear, and depression

inferior oblique

CIII oculomotor, and elevation

LR6 SO4 AO3

• LR6 = Lateral Rectus (CN VI - Abducens)

• SO4 = Superior Oblique (CN IV - Trochlear)

• AO3 = All Others (CN III - Oculomotor) (Superior rectus, Inferior rectus, Medial rectus, Inferior oblique)

"Super Man Is Late" (SMIL) for rectus muscles

Superior rectus = Moves up

Medial rectus = Moves in (medial/adduction)

Inferior rectus = Moves down

Lateral rectus = Moves out (lateral/abduction)

"Opposites rule!" for oblique muscles

Superior oblique = Moves eye down & out (depression, abduction)

Inferior oblique = Moves eye up & out (elevation, abduction)

Parasympathetic (rest & digest)

Constriction conserves energy, protects the retina, and aids in near vision.

Sympathetic (fight or flight)

Dilation improves vision in darkness and high-alert situations, preparing for action.

Rods

Night vision (black and white, high sensitivity)

Cones

color vision (red, green, blue)

bipolar cells

transmit signals from photoreceptors to ganglion cells

ganglion cells

form the optic nerve, send visual info to the brain

horizontal cells

enhance contrast and sharpness via lateral inhibition

amacrine cells

modulate signals, detect motion, adjust brightness sensitivity

RPE Cells

Absorb stray light, support photoreceptor function